In this mode, gpredict updates both uplink and downlink frequencies continuously and at the same time regardless of the RadioPTT setting

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In this mode, gpredict updates both uplink and downlink frequencies continuously and at the same time regardless of the RadioPTT setting &mdash; TBC: maybe I should use RadioPTT to decide whether we should correct which frequency to track when user changes dial?

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'''Pseudo Code'''

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'''Pseudo code'''

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<pre>

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To be written

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</pre>

== Implementation ==

== Implementation ==

Revision as of 23:11, 16 March 2009

Contents

Objectives

The first beta version of Gpredict 1.0 included a simple Doppler tuning algorithm that could adjust the receiver frequency and even take external frequency changes (e.g. tuning dial) into account. While it was a very good first cut at automatic Doppler tuning, the shortcomings were quickly identified. For example, it didn't take the PTT status for simplex radios into account and so Gpredict kept on sending RX correction commands to the radio even when the user was trying to transmit.

Clearly, a more sophisticated algorithm is needed and this page describes the design and prototyping of that algorithm.

Requirements

Gpredict shall be able to perform Doppler tuning for both uplink and downlink.

Gpredict shall be able to take external frequency changes into account, e.g. when the user turns the dial.

Gpredict shall be able to perform Doppler tuning using a receiver, a simplex transceiver, or a duplex transceiver.

Gpredict shall take into account that there might be transverters in the loop.

Operating Modes

The operating mode for the controller depends on what kind of radio is used. For now, the following options are considered:

Receiver Mode

The radio is only a receiver or a transceiver where tuning via CAT is only possible in receive mode. In this case, Gpredict shall perform Doppler tuning on the downlink only.

Simplex Mode

The radio can be tuned via CAT both in receive and transmit modes. Gpredict will perform Doppler tuning on the downlink and uplink depending on the PTT setting.

Duplex Mode

The radio is a full duplex transceiver like the IC-910H or FT-847. Gpredict will perform continuous Doppler tuning using VFO_MAIN for uplink and VFO_SUB on the downlink regardless of the PTT setting.

The Controller Algorithm

The control algorithm will need the following parameters:

Doppler

The current Doppler shift at 100 MHz.

SatRX

The downlink frequency at the satellite. This is set by the user on the Gpredict control panel or automatically if the uplink and downlink frequencies are locked, or if RadioRX is changed externally (e.g. via tuning dial).

SatTX

The uplink frequency at the satellite. This is set by the user on the Gpredict control panel or automatically if the uplink and downlink frequencies are locked, or if RadioTX is changed externally (e.g. via tuning dial).

RadioRX

The downlink frequency of the radio.

RadioTX

The uplink frequency of the radio.

RadioPTT

The PTT status of the radio. When available, this is used to switch between RadioRX and RadioTX tuning on simplex radios.

UsePTT

Flag indicating whether the PTT status on the radio should be polled and taken into acount (i.e. don't set RadioRX when RadioPTT = true).

PrevRX

The RadioRX frequency set during the previous cycle. This can be different than RadioRX in that the user may have turned the tuning dial since the last cycle.

PrevTX

The RadioTX frequency set during the previous cycle. This can be different than RadioTX in that the user may have turned the tuning dial since the last cycle.

There are also other user interface parameters like Engage and Track that influence the overall functionality, but these parameters are outside the scope of the controller algorithm.

Receiver Mode

In this mode the radio is used for reception only even if it is a transceiver. The reason could be that frequency setting via CAT is not possible in transmit mode as would be the case for the FT-817. If configured with UsePTT = true, gpredict will also poll the PTT setting and ensure that downlink correction are only set to the radio when RadioPTT = false.

Duplex Mode

In this mode, gpredict updates both uplink and downlink frequencies continuously and at the same time regardless of the RadioPTT setting — TBC: maybe I should use RadioPTT to decide whether we should correct which frequency to track when user changes dial?